U.S. stock futures on Tuesday signaled a small drop at the open, with analysts blaming the modest retreat on a raft of geopolitical worries, including former FBI boss James Comey's testimony to a Senate panel later this week.

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S&P 500 futures fell by 2.50 points, or 0.1%, to 2,432.00, while Dow Jones Industrial Average futures shed 22 points, or 0.1%, to 21,154.00. Nasdaq-100 futures gave up 1.25 points, or less than 0.1%, to 5,879.50.

Gold futures (http://www.marketwatch.com/story/gold-rises-looks-to-settle-at-7-week-high-2017-06-06) , the Japanese yen (http://www.marketwatch.com/story/dollar-falls-against-yen-as-analysts-see-flight-to-safety-due-to-geopolitical-fears-2017-06-06) and other safety plays were finding buyers, thanks in part to concerns about a spat between Qatar (http://www.marketwatch.com/story/saudi-arabia-bahrain-uae-sever-diplomatic-relations-with-qatar-2017-06-04) and other Middle Eastern nations.

Read: What you need to know about Saudi Arabia's break with Qatar (http://www.marketwatch.com/story/heres-what-you-need-to-know-about-saudi-arabias-spat-with-qatar-2017-06-05)

There are also jitters over three events on Thursday: the U.K. election, a European Central Bank announcement, and Comey's testimony before the Senate panel, which is investigating Russian efforts to interfere (http://www.marketwatch.com/story/nsa-report-says-russians-targeted-us-voting-infrastructure-alleged-leaker-arrested-2017-06-05) in last year's presidential race.

Read:What to watch when James Comey testifies to the Senate on Thursday (http://www.marketwatch.com/story/what-to-watch-when-james-comey-testifies-to-the-senate-on-thursday-2017-06-05)

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Geopolitical concerns are "helping to drive safe haven flow and curb risk appetite," said Richard Perry, a Hantec Markets analyst, in a note.

Check out: U.K. election -- the worst, best and most likely scenarios for stocks worldwide (http://www.marketwatch.com/story/uk-election-the-nightmare-best-case-and-most-likely-scenarios-for-stocks-worldwide-2017-06-01)

On Monday, the S&P 500 , Dow and Nasdaq Composite all finished lower by between 0.1% and 0.2% (http://www.marketwatch.com/story/us-stock-futures-brush-off-uk-terror-attacks-as-busy-week-kicks-off-2017-06-05), pulling back from all-time closing highs achieved Friday (http://www.marketwatch.com/story/us-stocks-poised-to-bust-out-new-records-as-optimism-about-payrolls-data-builds-2017-06-02).

Other markets: Oil futures edged lower, and European markets (http://www.marketwatch.com/story/european-stocks-set-for-1-week-low-as-caution-sets-in-2017-06-06) also lost ground. Asian equities finished mixed (http://www.marketwatch.com/story/asian-markets-slip-as-investors-turn-cautious-2017-06-05), and a key dollar index was slightly lower after earlier showing a bigger loss and touching levels last seen in November (http://www.marketwatch.com/story/dollar-falls-against-yen-as-analysts-see-flight-to-safety-due-to-geopolitical-fears-2017-06-06).

Economic news: An April figure for job openings is slated to arrive at 10 a.m. Eastern Time.

That fall came after Apple unveiled its HomePod smart speaker and other new offerings (http://www.marketwatch.com/story/apple-bets-that-youll-adopt-these-3-tech-habits-2017-06-05), and as Pacific Crest analysts downgraded the stock (http://www.marketwatch.com/story/apple-downgraded-as-analysts-say-investors-dazzled-by-iphone-8-arent-pricing-in-enough-risk-2017-06-05), saying all of the upside from the next iPhone is already priced in.

Amazon.com Inc.(AMZN) is dropping the price for its Prime membership for low-income shoppers (http://www.marketwatch.com/story/amazon-cuts-prime-fee-for-low-income-shoppers-as-it-takes-on-wal-mart-2017-06-06). The move is seen as taking aim at Wal-Mart(WMT) , which counts on shoppers who receive government assistance for a large percentage of its sales. Shares in Amazon edged lower in thin premarket trading.

Media giant 21st Century Fox Inc.(FOX) (FOX) is getting into the mobile videogame business, paying tens of millions of dollars for game studio Aftershock, a Wall Street Journal report said (https://www.wsj.com/articles/fox-buys-mobile-game-maker-aftershock-1496742304).

Struggling Toshiba Corp.(6502.TO) (6502.TO) has granted preferential negotiating rights for its semiconductor unit to U.S. chip maker Broadcom Ltd.(AVGO) , said a report from The Asahi Shimbun (http://www.asahi.com/ajw/articles/AJ201706060045.html), a Japanese newspaper.

Michaels Cos.(MIK) is among the companies expected to post earnings before the open.